A wide variety of indicators for measuring the pH of a cat's urine are known from the state of the art. As a rule, such indicators take the form of granules or small scraps of various kinds, such as small strips of paper, which are impregnated with a wide variety of pH indicators. These indicators react to a change in pH by changing colour.
EP 0 569 232 A1, for example, discloses a pH indicator material in which a coating made from an aqueous solution of a water-soluble polymer is applied to an inert core substrate, which coating likewise contains a sufficient quantity of a water-soluble pH indicator dye. Depending on the change in the pH of the urine, the pH indicator dye can alter its colour and thus indicate the change in the pH of a cat's urine.
Other indicator dyes for determining the pH of a cat's urine are known, for example, from U.S. Pat. No. 6,162,646, U.S. Pat. No. 6,019,062, U.S. Pat. No. 5,143,023, U.S. Pat. No. 5,371,054 and U.S. Pat. No. 6,376,252.
A major disadvantage of the indicator materials known from the state of the art is that the change in the colour of the indicator depending on the pH takes place continuously over a particular colour spectrum. In the case of the indicator dye bromine xylenol blue, for example, colour changes from an acidic pH to a basic pH are known over the colour spectrum yellow/greenish-yellow/yellowish-green/green/bluish-green/greenish-blue/blue.
The result of such a change in colour is as a rule susceptible of subjective interpretation, which means that each user might assess the colour change subjectively differently, such as whether the colour is still yellowish-green or already greenish-yellow. This makes it difficult to determine a change in the pH of the urine precisely.
The object the present invention is to provide an indicator material which overcomes the disadvantages of the state of the art, i.e. in particular which makes it possible to determine unambiguously whether the pH of the urine has changed beyond a threshold level. In addition, it is intended that such an indicator material should be capable of being used in a simple manner in a conventional cat lavatory.